1. Field of the Invention
The present invention relates to a hybrid module comprising a circuit board having a circuit pattern thereon and chip components such as a multilayer capacitor and a multilayer inductor, and semiconductor components respectively mounted on the circuit board, thereby constituting a circuit, more particularly to a hybrid module having a circuit board on which heat generating circuit components such as a field effect transistor and a power semiconductor device are mounted.
2. Description of Related Art
In a conventional hybrid module having a circuit board on which heat generating circuit components such as a field effect transistor and a power semiconductor are mounted, a special dissipating means is provided for dissipating heat from the circuit components. For example, in the hybrid module disclosed in JP-A 5-13627, a dissipating fin is provided on a circuit board, and heat generating circuit components mounted on the circuit board are connected with the dissipating fin via a thermally conductive member having a shape like a leaf spring. In this hybrid module, heat generated in the circuit components is discharged to the atmosphere via the dissipating fin.
There is another conventional hybrid module having a circuit board on which heat generating components are mounted as illustrated in FIG. 9. In this hybrid module, aluminum nitride is employed as a circuit board 1, and circuit components 7 and 7, each having a shape like a chip, are mounted on land electrodes 6 and 6 formed on the circuit board 1, and further, a circuit component 3, such as a heat generating semiconductor device, is mounted on the land electrodes 4 and 4 via a soldering bump 5. The circuit board 1 is mounted on a mother board (board 9) and terminal electrodes 8 and 8 of the circuit board 1 are connected with land electrodes 10 and 10 formed on the mother board (board 9). Further, the circuit board 1 and mother board (board 9) are connected with each other at opposing surfaces thereof via a conductive film 2 which has a good thermal conductivity and is formed on the mother board (board 9).
Aluminum nitride is noted as an insulating material having good thermal conductivity. In the aforementioned hybrid module, heat generated in the circuit component 3 mounted on the circuit board 1 is transmitted to the mother board 9 via the circuit board 1 respectively made of aluminum nitride and conductive film 2 and is dissipated.
In the abovementioned hybrid module disclosed in JP-A 5-13627, heat which is generated at the circuit component 3 via the dissipating fin is dissipated in the atmosphere, and hence the surface area of the dissipating fin is inevitably required to be as large as possible to enhance the heat dissipating efficiency. Accordingly, a space occupied by the dissipating fin is made large in the hybrid module, which causes a problem that the hybrid module is difficult to miniaturize.
On the other hand, the aforementioned other hybrid module as illustrated in FIG. 9 dispenses with a dissipating fin because heat generated in the electronic device 3 is dissipated to the mother board 9 via the circuit board 1, and also the space occupied by the dissipating fin is omitted, namely, the hybrid module is not enlarged in its capacity because the circuit board 1 serves also as a heat dissipating or dissipating means. However, although alumina nitride has a good thermal conductivity, it is very expensive compared with a general substrate material made of, for example, alumina, which causes a problem of high cost.